The need for greater bandwidth and higher data transmission rates has motivated efforts to develop next-generation platforms for information storage and delivery. It is widely believed that optical information systems will provide superior performance to today's microelectronics-based systems. Integrated optical systems based on silicon photonics are a leading replacement technology for microelectronic systems. The silicon photonics platform interfaces with standard CMOS technologies and WDM (wavelength division multiplexing) to convert electrical signals to optical signals, transmit optical signals, and reconvert optical signals to electrical signals. In disaggregated systems, transfer of signals between units occurs through optical links that provide high modal bandwidth and high data transfer rates.
Low-loss coupling between optical fibers and transceivers is a key challenge for data centers and high performance computing applications. In order to operate efficiently, losses in the transfer of optical signals to and from the optical links and devices used in integrated optical systems need to be minimized. Efficient coupling of optical signals is needed between the light sources, chips, waveguides, fiber, and receivers used in systems as well as in the links for delivering optical signals.
Of particular interest is efficient coupling of optical signals to components used in silicon photonics technology. A typical optical data link in silicon photonics includes a light source formed in or on a silicon substrate that generates an optical signal embodying data, an optical fiber for transmitting the optical signal, and a detector for receiving the optical signal, where the detector is formed in or on a silicon substrate. The light source and detector are “on-chip” devices and efficient coupling of optical signals between the chips and the interconnected optical transmission fiber is needed to enable the technology platform. The chip containing the light source may be referred to herein as a transmitting chip and may also include devices for receiving electrical signals and converting electrical signals to optical signals. The chip containing the detector may be referred to herein as a receiving chip and may also include devices for converting optical signals to electrical signals.
Efficient coupling of optical fibers to on-chip devices is challenging because many promising applications of silicon photonics technology require implementation in confined spaces. To minimize system size, it is often necessary to deploy the optical fiber in a highly bent configuration. The optical fiber must accordingly be resistant to macrobending losses over a wide range of bending angles. In addition, the optical fiber must exhibit low microbending losses.
A variety of techniques to reduce coupling losses of optical fibers to transmitting and receiving chips have been proposed. Most techniques use lenses and light-steering elements to form an optical bridge between the transmission fiber and the transmitting and receiving chips used for optical data transmission. To date, however, progress has been limited and achieving coupling loss less than 2 dB has proven to be formidable challenge. There is a need for new techniques for improving coupling efficiency between components in integrated optical systems.